Basic Cisco questions

I'm currently involved in the acquisition and basic design of a very typical Cisco core/distrubution/access layer campus network. But since I'm rather new in this area I have a few basic design questions.

1. Can anyone explain me why you strictly need one (or better 2) core switches (Catalyst 4500 or 6500) with a supervisor module?
2. What is the supervisor doing exactely?
3. Why do you need 2 of them?
4. What happens when you only have one and lose that one? Your network stops working?
5. Can you build the network without a 4500 or 6500 core switch? What would be the consequence of not having a core switch?
6. Why is it so expansive?
7. What is the difference between the Base and the Lite image in the 2960 and other series? Is there a big difference in price? In what cases is the Lite image sufficient?

From a design perspective, engineers design networks with scalability in mind, and more importantly, for resiliency. The core network is designed to switch packets as fast as possible; the backbone (Core network) is to connect regional distribution networks and, in some instances, to provide connectivity to other peer networks. In a network design build, there is a basic need for resilience in the backbone, a good starting point for the backbone topology is a ring connecting all distribution networks. Additionally, if there is no other POPS, peer networks, or any other infrastructure to connect the core network to, you still build/design a network with core devices for scalability. Obviously cost is important, so you can also collapsed the core into the distribution layer to allow the same functionality. The only difference is you are moving your core routing protocols into the distribution layer which can be migrated/integrated into a dedicated core layer design build later on in the future.

The use of MLS switches such as the 4500/6500 with supervisor modules if for the requirements of fast packet switching; this is typically accomplished with IP CEF, specifically with dcef utilizing 6500 series switches. There are many routers/switches that can be used in the core layer, such as the GSR series routers which I have seen replaced with the 7600 series routers. Depending on the bandwidth and traffic requirements, the design build could also include the 6500 series as well. The supervisor module, assuming the SUP720 which includes the MSFC and PFC, switch fabric, etc is used for the switching, policy and routing engines. Utilizing a switch architecture with dcef is where the fast switching comes in, and this is the primary goal of the core network layer.

2. What is the supervisor doing exactly?

Everything! It is very complex architecture with specialized ASICS that handles routing, switching, ACL lookups with features such as IPv6 in hardware, QoS, MPLS, etc. It is the heart of the 6500/7600 series devices.

3. Why do you need 2 of them?

You don't "need" two of them; however, if you are not building the network with dual devices (Dual core, Dual distribution, etc), then it is recommended that if you have a single router/switch for the core network, that you utilize 2 SUP engines for redundancy.

4. What happens when you only have one and lose that one? Your network stops working?

Yes, as already stated, it is the heart of the 4500/6500

5. Can you build the network without a 4500 or 6500 core switch? What would be the consequence of not having a core switch?

Yes, you can; however, depending on the business model, the design may require the implementation of a core network for fast routing/switching. Again, the core network is design to route/switch your packets as fast as possible without having to worry about ACLs, policy routing, QoS, etc. The idea is to look at the CEF table and just switch, nothing more nothing less.

6. Why is it so expansive?

As already quoted, the SUP720 and other variants have specialized ASICs and memory that is very costly and the design (Component level engineering was very complex); yes, it is expensive, but the business case and requirements will ultimately drive what components the network requires in the end.

7. What is the difference between the Base and the Lite image in the 2960 and other series? Is there a big difference in price? In what cases is the Lite image sufficient?

It depends on your requirements and what features you need in your network, example:

The Core is just that - the "heart" of the network. If it dies, everything dies. That is where the money is spent to keep everything humming. Dual power supplies, dual supervisor engines, maybe even dual chassis in a VSS pair. If your business looses 1M a day if the network is down, then you need to spend whatever it takes to keep it up. If your business can stand to have the network down for a week without really losing business, then you spend accordingly.

6. Why is it so expansive?
"Expensive" is a relative term.

Just an example - say an emergency 911 call center needs to be up 24/7/365 without fail. Lives literally hang in the balance if calltaker cannot access data, or dispatch first responders because the network is down. How much is your daughter's life worth if she is the one wrapped around a tree in an auto accident and tries to call 911?
How about the production line of a major manufacturer? Many have contracts with other manufacturers like , oh, I don't know, like Mercedez Benz. They have agreements and contracts for "just in time delivery" with MAJOR $$ penalties if they don't deliver the seats to MB right on time every time. How much do you spend to keep the production line humming? Would $2M be too much if the penalties could range into 10's of millions?
On the other hand, maybe the business is something like a public library. Yes, the network is essential to keep the flow of books moving around, and provide essential Internet access to a small public group, but if the network does go down for a day or so, is any real revenue lost? Is anyone's life in jeopardy?

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Stephans2Author Commented: 2011-03-20

OK, thank you both for your answers. The thing is we are talking about a mid sized (2000 users) public university in Peru and our budget is limited and I just wanted to make sure we are making the right investment choices.

In this case none of these conditions are met. It's an organisation that does not loses a 1M a day when the network is down and no ones life is threated when the network is down.

Of course the vendors try to sell us the most expensive solution they can and I wanted to make a more informed choice since I'm not designing a Cisco network every week. :-)

I know it's all about requirements but sometimes it's difficult to define and hard to find out. And since I wanted to keep the question general I didn't elaborate on the specific situation. But at least now I know a little bit more.

One other question: Both the Juniper and Cisco vendors are juggling with "special" discounts (since we are an public academic institution) on the products. I found a website that has Cisco list prices for the US. But can I find them somewhere for Juniper products? I mean real official list prices?

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In this case none of these conditions are met. It's an organization that does not loses a 1M a day when the network is down and no ones life is threated when the network is down.

True, but, an engineer would never design a network without requirements, this includes everything that has been mentioned. As already stated you do not need dual routers/switches in every campus building unless this is a requirement. As a matter of fact, if there are budget constraints then you could always merge all 3 layers (Core, Distribution, and access) into one layer with a 4500/6500 and design with one chassis and dual SUPs in mind.

Of course the vendors try to sell us the most expensive solution they can and I wanted to make a more informed choice since I'm not designing a Cisco network every week. :-)

I hear ya, they are like vultures flying around your head! All I can say is review all your requirements; security, redundancy, bandwidth, routing protocols, CPU, memory, etc and design a business case with a few pages on cost analysis

I know it's all about requirements but sometimes it's difficult to define and hard to find out. And since I wanted to keep the question general I didn't elaborate on the specific situation. But at least now I know a little bit more.

Understood, it is very difficult to define and these most time consuming phase of network design. This is where as an engineer you talk to management, staff, users, etc and understand the business model, work flow statistics, type of network applications in use, etc and this is where the requirements are built from.

I found a website that has Cisco list prices for the US. But can I find them somewhere for Juniper products? I mean real official list prices?

Thanks for your answers again. That's the list I found too. But it dates back to jan 2010. It's hard to find both Cisco and Juniper official list prices. They handle it like it's the biggest secret apparently. I don't understand why though...

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